Mobile joint suitable for a sitting device

ABSTRACT

The present invention relates to a mobile joint ( 1 ) with spring resistance, suitable for a sitting device, comprising a first and a second joint element ( 10, 20 ), which are pivotally connected by a shaft ( 3 ), to allow tilting of the sitting device caused by the displcement of the users weight, comprising a first and a second parallel plate spring ( 18, 19 ) with first and second ends, with an intermediate blocking element ( 11 ), wherein each plate spring ( 18, 19 ) in the first end are connected to the first joint element ( 10 ), and in the second end are glidingly abutting the second joint element ( 20 ), the first and second plate spring ( 18, 19 ) each having an axis of rotation that is displaced in relation to each other and the shaft ( 3 ).

FIELD OF THE INVENTION

The present invention relates to a simple and compact moveable jointwith spring resistance suitable for use in furniture such as a chair.

PRIOR ART

Several types of chairs comprising moveable joints connecting a seat andan underframe are known in the art, particularly in office chairs. Thesechairs often have a resting position and two extreme end positions, astooping position and a more laid-back position. The chairs are oftenprovided with a complex joint comprising spring means, in order toobtain the ability to tilt the chair seat between the said positions,and to bring the seat back to its intermediate resting position.

For example, FR 2267068 describes a conventional joint used in officechairs wherein a leaf spring is used to provide resistance against thetilting action. However, this type of joint using steel leaves, isdependent on several leafs of relative great lengths in order to providethe mentioned resistance. The joint is therefore highly visible,difficult to integrate in furniture, such as a chair, and produces alarge spring travel. In addition the joint according to FR 2267068 onlyprovides resistance in one tilting direction and has no stopping devicelimiting the swing.

Furthermore, numerous different armchairs and recliners exist withtilting backrest wherein pivoted joints or rails in differentembodiments are used to provide a similar movement. Friction- or springmeans may be used to provide resistance to such movement. The mechanismsin these chairs to tilt the chair seat are also complex and sometimesvisible on the furniture.

Joints of this kind have also been integrated in the seat of the chairutilizing the padding of the seat to provide a spring-like effect to thejoint. This makes it possible to create a joint which is less complexand smaller. The problem encountered with this solution is thatrelatively large forces must be absorbed by the padding material withoutdeformation; hence the material must be relatively compact to providesufficient resistance. Padding of this kind is not particularlycomfortable and it has proven difficult to provide a padding which alsohas sufficient strength. To obtain sufficient strength, an alternativesolution has been to compensate with additional padding, but thisresults in a bulkier piece of furniture and affects the appearance ofthe furniture.

In GB 1299740, a joint is described with a stiff elastic paddingproviding resistance against the tilting of the two joint elements.However, this solution provides a very limited and imprecise tilting andalso allows an unfavourable rotation in the horizontal plane of thejoint elements in relation to each other. The padding is subjected toaging and wear, especially when under tension, which changes the elasticproperties of the padding. With time, the joint will end up resting onthe main bolt connecting the two joint elements and subjecting it todamageable wear, if not regularly tightened. Such tightening will againrestrict the tilting angle.

Tilting of a chair seat is desirable for several reasons. In officechairs, the chair adapts better to the sitting position of the userdepending on the users movement. Such a dynamic and varying sittingposition is more ergonomically favourable for the body than a staticsitting position. Tilting of the chair seat therefore feels morecomfortable, and gives the user a feeling of quality since the chair isless strenuous to sit on.

It is therefore desirable to pursue this quality in simpler chairs suchas chairs for use at dining tables or conference chairs etc. Thedisadvantage of current solutions is that the joints are complex andheavy devices which are not easily adapted to chairs where a simpledesign, light weight and for example the possibility to stack thechairs, is desired.

Thus, there is currently a need for a small and simple joint with springresistance, being light in weight, for simpler chairs where the seat andoptionally the back of the chair may be tilted to extreme positions, andreturn to a rest position when the chair is not in use.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a joint for a chairwhich eliminates the above problems and addresses the deficiencies thatearlier solutions had.

The object of the invention is achieved by a mobile joint (1) withspring resistance, as defined in the patent claims, suitable for asitting device, comprising a first and second joint element (10,20),which are pivotally connected by a shaft (3), to allow tilting of thesitting device caused by the displacement of the users weight,comprising a first and second parallel plate spring (18,19) with firstand second ends, with an intermediate blocking element (11), whereineach plate spring (18,19) in the first end are connected to the firstjoint element (10), and in the second end are glidingly abutting thesecond joint element (20), the first and second plate spring (18,19)each having an axis of rotation that is displaced in relation to eachother and the shaft (3).

The joint according to the present invention consists of few parts,provides novel use of materials such as glass fibre or compositematerial in the springs thus enabling a compact joint with goodfunctionality in relation to wear.

The joint provides great stiffness with only two spring elements, aswell as small spring travel providing good resistance againstexhaustion. In addition the plate springs of the present joint mayeasily be changed for repair or adaptation to the user.

The joint of the present invention may have a near cubic form and mayeasily be fitted in a variation of constructions and be mounted upsidedown, side ways or in any other angle.

The joint may therefore be produced and assembled at low costs bystandard production equipment, which may easily be automated, andrepresents low costs in transportation and storage due to its small sizeand light weight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a phantom view of a chair with a joint according to theinvention integrated in a chair seat and attached to an underframe.

FIG. 2 shows a perspective view of the joint shown in FIG. 1.

FIG. 3 shows a section of the joint in rest position.

FIG. 4 shows a section of the joint in FIG. 1 in an alternativeposition.

FIG. 5 shows a section of the joint in FIG. 1 in an alternativeposition.

DETAILED DESCRIPTION

A preferred embodiment of the invention will now be described in detail,with reference to the figures. The embodiment is an example of theinvention and is not intended to limit the scope of the invention.

In the following description the expressions “front” and “forward”describes the direction the user faces when she or he is seated withtheir back towards the back of the chair in a normal way, and theexpressions “rear” and “back” refer to the opposite direction, unlessotherwise stated.

Furthermore, reference to the angle of the joint refers to the anglebetween the seat surface and the ground, e.g. the floor. In thedemonstrated embodiments, this angle corresponds to the angle betweenthe upper and the lower face of the described joint, but this will notalways be the case in alternative embodiments of the joint.

EXAMPLE EMBODIMENT

As shown in FIG. 1, the joint 1 according to the invention, is suitableas a connecting joint between a chair seat and an underframe 200. Theunderframe 200 comprises four legs joined in an upper mounting suitableto attach the seat of the chair.

In this embodiment, the joint 1 is designed as shown in FIG. 2,comprising two joint elements, one lower joint element 10 and one upperjoint element 20 which are jointed via a horizontal shaft 30. The upperjoint element 20 can be tilted between two extreme positions in relationto the lower joint element 10 which it is connected to.

The lower joint element 10 in this embodiment is substantially parallelto the surface. The lower joint element 10 will be arranged to anunderframe 200.

The upper joint element 20 will be arranged to the seat of the chair,and is substantially parallel to the seat of the chair. A frame 50 ismoulded within the padding of the chair and constitutes the means ofattachment of the seat 100 to the upper joint element 20. In thisembodiment the joint is integrated in the seat 100 of the chair.Advantages of an integrated joint are that crush injuries are prevented,no dirt enters into the joint and the furniture obtains a better visualappearance.

As an alternative, the upper face of the upper joint element 20 isapplicable as an attachment face to the lower face of a chair seat orsome other kind of fixture for the seat.

The joint 1 may be positioned in three main positions depending on theposition of the centre of gravity of the user relative to the shaft 30,by the tilting of joint elements 10 and 20 in relation to each other.

In FIG. 3 the joint 1 is shown in the rest position where the centre ofgravity 300 of the user is positioned in line with the shaft 30. Hencethe joint 1 has a starting position α (between the upper face 21 of thejoint and the surface), which can be any angle which is appropriate forthe intended use, which in this embodiment for example is about 0° whenthe chair is used in an upright position.

As shown in FIG. 3 the lower joint element 10 is formed as a base with arising block element 31 to which the shaft is connected through and twoplate springs 18 and 19 on each side of the block element 11 parallel tothe shaft 30. The springs 18 and 19 are based to the lower part of thelower joint element 10 by means of through bolts 14 transverse to theshaft 30.

In FIG. 4 the joint is shown in a forward tilted position, where thecentre of gravity 300 of the user is positioned in front of the shaft30. In this position the joint has an angle β, which in this embodimentfor example is 8°. The spring 18 will in a forward tilted position likethis provide a resistance to forward tilting of the upper joint element20 due to the abutment of the abutting face 22 on the spring 18. Theupper joint element 20 may be tilted forward until the spring 18 (andthe upper joint element 20) abuts the rising block element 11. Todistribute the tension on the spring 18, the abutting face of the blockelement is curved.

In FIG. 5 the joint 1 is shown in a backward tilted position where thecentre of gravity of the user is positioned behind the shaft 30. In thisposition the joint has an angle θ, which in this embodiment for exampleis 8°. The spring 19 will, in the same manner described above, provideresistance to tilting of the upper joint element due to the abutment ofthe abutting face 23 on the spring 19. The upper joint element 20 may betilted backwards until the spring 19 (and the upper joint element 20)abuts the rising block element 11 with the curved abutting face 13.

Hence the joint 1 possesses a spring resistance, which forces the upperpart 20 towards its resting position and moves the chair back to thestarting position when no force is exerted on it by the user.Furthermore, the springs 18, 19 will cushion the movement in joint 1 andprovide smooth movement between the main positions. This providescomfortable movement and an improved preventive measure to avoid cantingthe chair.

Generally, the resistance of the spring should be adapted to the weightof the user, the weight of the seat, the angle between the seat and theback of the chair, and the assembly position of the seat relative to thejoint.

The spring resistance in joint 1 is provided by springs 18, 19, whichare preferably made of fibreglass. These springs may be produced veryrigid, and are adjusted according to the conditions outlined above. Theresistance of the springs can be adjusted by altering the thickness andwidth of the springs, the length or the height of the spring andoptionally the joint, and the composition of materials in the spring.Optionally, the spring resistance may be adjusted by altering thedistance between the shaft 30 and the fixings 14 of the springs 18, 19.

The rigidity of the fibreglass springs makes it possible to design amore compact joint compared to a similar joint using springs of steel.Preferably the springs are made of fibreglass, wherein different typesmay be utilized, and may be reinforced with different materials such ascarbon, Kevlar etc.

The inflection of the spring 18, 19 does not start at the level of theshaft 30 but is displaced from this level. This allows a longer curve ofthe spring than in usual conventional spring joints for chairs. Due tothe difference in length of the lever of rotation for the spring 18, 19and for the upper joint element 20, a certain transmission ratio isprovided between the spring 18, 19 and the upper joint element.

The curved abutting faces 12, 13 are important to prevent the spring 18,19 being over-stressed due to high stress at the fixing to the lowerjoint element 10, resulting in fracture of the spring.

Due to the displacement of the axis of rotation 30 of the joint at theshaft 30 in relation to the fixing of the springs, the springs willslide on the abutting faces 22, 23 of the upper joint element 20. Hence,a protective barrier may preferably be provided between these parts.Such a protective barrier can prevent wear and rubbing noises andoptionally clicking noises, created by the contact between the abuttingfaces 22, 23 and the spring during rotation of the joint.

The lower joint element 10 may be provided with parts of a fixture, suchas a guide means, to attach the joint 2 to a possible base or anunderframe.

Likewise, the upper joint element 30 may be provided with an upper face31 designed for attachment to a chair seat, for example by way of boltsand/or a rail device.

The preferred embodiment of the joint depends on the design of the chairseat, the angle of the back, the weight of the seat, the weight of theuser, and possible limitations due to the design of the underframe.Furthermore, the relation of angles and distances will be affected bythe resistance of the springs and the angle and the stiffness of thespring. In the above embodiment the size of the joint is for example 8cm×10 cm×8 cm (height×width×length) in a start/resting position, andform a very compact joint. The joint parts 10, 20 can be made of anysuitable material such as a metal, plastic material or a composite,preferably a metal such as steel or aluminium.

ALTERNATIVE EMBODIMENTS

In the above embodiment, the joint element is constructed such that thelower joint element 10 comprises a block element 11, which protrudesinto the upper joint element 20, but the opposite is obviously alsopossible and the joint may be installed “upside-down”. Hence, the upperjoint element 20 may be provided with one or more block elements whichprotrude into the lower joint element 10, with corresponding abutmentfaces. Furthermore, a block element may comprise several protrudingblock elements which cooperate with corresponding structures in facingjoints, such a construction may provide further abutting faces andrenders a larger area of contact.

In an alternative embodiment the allowed backwards tilt angel can begreater than the allowed forward tilt angel. Furthermore, the resistanceof the springs may be greater forwards than backwards, or vice versa.The deflections can be varied to accommodate any use, and may forexample be in the range 5-10°.

In another alternative embodiment each spring 18, 19 may be divided intotwo or more parallel spring blades with different thicknesses inrelation to each other. In this embodiment, the spring resistance willbe progressive as the upper joint element 20 is rotated and connectswith more spring blades subsequently during rotation. Alternatively, theparallel spring blades may be displaced in relation to each other, withdifference in distance to the shaft 3, to obtain a similar effect.

Furthermore, the joint according to the invention may be used for anychair seat or furniture having any design. Such a chair may also be onewithout a back, e.g. a stool, where the user has a sitting positionsupported both at the knees and the behind.

Furthermore, the underframe may have any design and several chairs withjoints 1 may for example be mounted in a row onto the same underframe toprovide a bench-like row, a row of seats in a stadium, a cinema or atheatre etc.

1. A mobile joint (1) suitable for a sitting device, comprising a first and second joint element (10,20), which are pivotally connected by a shaft (3), to allow tilting of the sitting device caused by the displacement of the users weight, characterized in that the mobile joint comprises a first and second parallel plate spring (18,19) with first and second ends, with an intermediate blocking element (11), wherein each plate spring (18,19) in the first end are connected to the first joint element (10), and in the second end are glidingly abutting the second joint element (20), the first and second plate spring (18,19) each having an axis of rotation that is displaced in relation to each other and the shaft (3).
 2. The Mobile joint (1) according to claim 1 characterized in that the springs (18, 19) abut curved faces (22, 23) on the blocking device (11) when deflected.
 3. The Mobile joint (1) according to claim 1, characterized in that the spring is adjustable by adjusting the distance from the axis of rotation of the shaft (30) to the fixing of the springs (18, 19).
 4. The Mobile joint according to claim 1, characterized in that the springs are made of fibreglass.
 5. The Mobile joint according to claim 4 characterized in that the fibreglass is reinforced by means of carbon and/or KEVLAR.
 6. The Mobile joint according to claim 1, characterized in that the springs are divided into two or more parallel spring blades having different thicknesses in relation to each other, and/or, are differently displaced in distance to the shaft 3, providing progressively increasing spring resistance as the upper joint element 20 subsequently connects with more spring blades during rotation.
 7. The Mobile joint according to claim 1, characterized in that the outside dimensions of the joint (1) is approximately 8 cm×10 cm×8 cm (height×width×length).
 8. The Use of the mobile joint (1) formed according to one of the preceding claims in a chair comprising a seat device (100) and an underframe (200) wherein the mobile joint (1) connects the seat device (100) and the underframe (200).
 9. The Use according to claim 8 wherein the mobile joint (1) is integrated in the seat device (100). 